Heat recoverable articles have found widespread acceptance in employment as seals or other closures in the repair and protection of generally tubular conduits such as pipe joints and electrical conductors. Typically, such articles have comprised heat recoverable tubular sleeves which describe in cross-section an integral, closed curve. Among the heat recoverable sleeves so-configured are those produced according to U.S. Pat. Nos. 3,086,242 and 2,027,962, the disclosures of which are incorporated herein by reference.
While such sleeves are generally satisfactory in many applications, they require first the provision of a free end in the conduit to be protected, over which the sleeve can be slipped. That manner of application is often manifestly inconvenient. For example, where a secondary electrically conductive line is to be tapped or spliced into a primary carrier, it is desirable that the splice be protected by application of a sleeve which does not require for its placement the disengagement of the existing carrier. Again, where a conduit carrying gas, water or other fluid cracks, it is desirable to stop the resultant leakage by application of a sleeve which for its placement does not require creation of a break in the pipeline and removal of the damaged conduit therefrom. To the same extent, it is desirable to repair cracks in cable insulation without necessitating the provision of a free end by breaking the cable.
It has been proposed to form wrap-around closures which for their application do not require a free end of the substrate to be protected, the closures being formed from a heat recoverable tube which is longitudinally slit, placed about the substrate, edge-joined by mechanical means, and heat-recoverd to a snug, sealant configuration. See for example U.S. Pat. Nos. 3,455,336 and 3,379,218, the disclosures of which are incorporated herein by reference. While those closures have to a great degree lessened the difficulties related above, the need remains for a wrap-around heat recoverable sleeve which can be quickly and conveniently applied without resort to the additional positive steps required for mechanical joinder of closure edges. That need has been met in a large part by the invention disclosed in the concurrently filed application of Sovish, et al, assigned to the assignee of this application Ser. No. 130,678, filed Apr. 2, 1971 (and since abandoned in favor of divisonal application Ser. No. 348,348, filed Apr. 5, 1973) and now U.S. Pat. No. 3,899,807 the disclosure of which is incorporated herein by reference. That application discloses articles rendered involutely heat recoverable by lamination of a first heat recoverable layer to a second, relatively non-heat recoverable layer which resists linear recovery of the first such that the laminated article curls upon recovery. While admirably meeting problems raised by the prior art, however, the invention of Sovish, et al, suffers the disadvantage of requiring a plurality of laminae.